Take a look at the attached file: this is an example of a DNA sequence trace file.
In this pdf, we see part of a DNA sequence of a mutant plasmid (about 1180 nucleotides). The purpose of this trace file is to check if the insert (mutation) was transferred into the plasmid or not.
To verify this, we just need to know that there is a nice, tall peak at the spot where the mutation is supposed to be. Then, based on the color of the peak, we can also see if the correct nucleotide (A, T, C, or G) was replaced.
(black=G, red=T, blue=C, green=A)